Indications
Nirmatrelvir is an antiviral medicine used, together with a low dose of Ritonavir, to treat mild to moderate COVID-19 in adults (and some adolescents) who are at high risk of becoming seriously ill, for example because of older age, diabetes, heart, lung or kidney disease, obesity or a weak immune system. It should be started as soon as possible after a positive test, within 5 days of symptoms starting. It is not used to prevent COVID-19 and does not replace vaccination.
How It Works
Nirmatrelvir blocks an enzyme of the coronavirus called the main protease (3CL protease), which the virus needs to make working copies of itself. This stops the virus from multiplying. Ritonavir has no useful effect on the virus at this dose; it slows the breakdown of nirmatrelvir in the liver so that it stays in the body at effective levels.
Dosage and Administration
The usual adult dose is 300 mg of nirmatrelvir (usually two 150 mg tablets) taken together with 100 mg of ritonavir, twice a day for 5 days, with or without food. People with moderate kidney impairment take a reduced dose (usually 150 mg nirmatrelvir with 100 mg ritonavir twice a day), as prescribed. Swallow tablets whole and complete the full 5 day course even if you feel better.
Interactions
Because of the Ritonavir, this treatment interacts with many medicines, some dangerously. Always tell the doctor or pharmacist about every medicine and herbal product you take.
- Must not be combined with certain medicines, including Amiodarone, Simvastatin, Lovastatin, Rifampicin, Carbamazepine, Phenytoin, St John’s Wort, Sildenafil for lung hypertension, Midazolam taken by mouth, Colchicine in kidney or liver impairment, and some antipsychotics and heart rhythm medicines.
- Doses of other medicines, such as Atorvastatin, Rosuvastatin, some blood thinners, Tacrolimus, Ciclosporin, some calcium channel blockers and some pain medicines, may need adjusting or pausing.
- Hormonal contraceptives may be less effective; use a barrier method during treatment and for one cycle after.
Contraindications
- Allergy to Nirmatrelvir or Ritonavir.
- Severe kidney or liver impairment.
- Use with medicines that strongly depend on CYP3A for clearance or that strongly induce CYP3A, as listed by your doctor.
Side Effects
Common effects are a change or bitter taste in the mouth, diarrhoea, nausea, vomiting, headache, raised blood pressure and muscle aches.
Get urgent medical help if you have signs of an allergic reaction (rash, hives, swelling of the face, lips or throat, difficulty breathing), yellowing of the skin or eyes, dark urine, or if your COVID-19 symptoms become severe, such as breathlessness or chest pain.
Pregnancy and Lactation
There is limited information in pregnancy; it is used only if the doctor decides the benefit outweighs the risk. Breastfeeding should be avoided during treatment and for 7 days after the last dose.
Precautions and Warnings
- Kidney function should be known before prescribing.
- Use with care in liver disease.
- In people with untreated or uncontrolled HIV, ritonavir may lead to HIV drug resistance.
- Symptoms may return briefly after the course ends in some people; isolate as advised and contact your doctor if unwell.
Overdose
There is limited experience. If too much is taken, contact a doctor or go to hospital for monitoring and supportive care.
Therapeutic Class
Antiviral, SARS-CoV-2 main protease inhibitor (with Ritonavir as a pharmacokinetic booster).
Storage
Store below 30°C in a dry place, away from light, in the original blister pack and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.